1. Field of the Invention
Aspects of the present invention relate to a secondary battery, and more particularly, to a secondary battery that is free from appearance imperfections resulting from welding.
2. Description of the Related Art
In general, lightweight, high-performance portable devices, such as video cameras, mobile phones, notebook computers, and so on, use secondary batteries as portable power sources. Secondary batteries include nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries, lithium secondary batteries, and so on. Lithium secondary batteries have become popular power sources because they are compact, have a large capacity, a high operating voltage, and a high energy density per unit weight.
A lithium secondary battery can be formed by: inserting an electrode assembly, including a positive electrode plate, a negative electrode plate, and a separator, into a can; attaching a protection circuit board to the electrode assembly; sealing an opening of the can with a cap assembly, and covering the can with a cover or label.
The lithium secondary batteries are classified as cylindrical, prismatic, or pouch-type, depending on the shape of the can accommodating the electrode assembly. A lithium secondary battery includes an electrode lead to electrically connect the electrode assembly to the protection circuit board. In cylindrical batteries, the electrode lead can be welded to the can, to form an electrical connection to the electrode assembly.
When the welding is performed at the bottom part of the can, since the electrode lead is elongated along side surfaces of the can, an adhesive tape is needed to attach the bare cell to the electrode lead. In addition, since the can is formed of an aluminum material, the aluminum material may be damaged, due to pressure and heat during the welding, which can affect the appearance of the secondary battery. Further, when the protection circuit board is installed at the top end of the can, since the cap-up is below the protection circuit board, due to the thickness of the protection circuit board, it is difficult to use the cap-up as an external terminal.